1. Field of the Invention
The present invention describes a method for the hydrogenation of 4-oxo-2,2,6,6-tetramethylpiperidine (triacetoneamine, TAA) to give 4-hydroxy-2,2,6,6-tetramethylpiperidine (TTA-ol) and a catalyst suitable for use in the method. The catalyst can be arranged as a fixed bed in a continuous process, and can be used discontinuously as a powder in a batch process, in accordance with the present invention.
2. Discussion of the Background
Numerous catalysts are known from the literature for the preparation of 4-hydroxy-2,2,6,6-tetramethylpiperidine. For example, the use of nickel catalysts is described in Czechoslovak Patent Nos. 235,486, 235,487 and 236,437. TAA is used in each case as an alcoholic solution (for example, in isopropanol and isobutanol). Other catalyst-solvent combinations are mentioned in other patent documents. In DE-A 2,656,765, Ciba Geigy proposes the use of nickel catalysts and noble metal catalysts in the solvents such as toluene, xylene and ethers; in DE-A 2,656,764, Ni and Ru as catalyst and water as solvent; in DE-A 2,656,763, Ni and noble metals (Ru, Rh, Os, Ir, Pt) as catalyst metals and tri-n-alkyl phosphates as solvents; in EP-A 225,850 and EP-A 375,612, Ru as catalyst and water or alcohols as solvent. Finally, EP-A-290,387 claims a hydrogenation process in the presence of a metal catalyst selected from the group comprising Ni, Co, Ru, Rh, Os and Ir, in the absence of a solvent. Ni and Ru catalysts are preferred.
Previous processes for the hydrogenation of TAA to give TAA-ol are known to have considerable disadvantages. Such disadvantages include complex procedures required for the separation of by-products, waste water pollution and losses of both product and solvent.
From both ecological and economic points of view, it is necessary that the hydrogenation of TAA to give TAA-ol proceeds with complete conversion and very high selectivity. When these conditions are met, the losses of TAA-ol are small, and only very small quantities of by-products are formed. As a result, solvents (if present) can be completely recycled.